By combined use of immunochemistry, lipid model membranes, and biophysical techniques such as membrane probe spectroscopy (EPR and fluorescence), black-lipid membranes, and lipid monolayer techniques, it is proposed to investigate the molecular events that occur during complement mediated membranolysis. The function of the membrane attack complex (MAC) of complement will be investigated with respect to penetration into membranes, formation of a protein-walled channel across the membrane, reorientation of ordered bilayer lipids, and interaction with other membrane proteins. The virolytic action of MAC proteins will be studied in particular. A fuller understanding of the role of complement in the body's immune defense system will undoubetedly open the way to new and better means of controlling infections, allergic disorders, and autoimmune diseases.